When testing a computer program, a user may input samples of test data (e.g., textual samples, numerical samples, etc.) to the computer program to determine whether the program properly handles the samples. One approach to testing the computer program uses positive samples. For example, if the computer program is to behave in a particular fashion upon receiving a sample in a particular format, samples in the particular format may be referred to as positive samples, and may be used to ensure that the computer program behaves as expected. Another approach to testing the computer program uses negative samples. In the above example, a negative sample is a sample that does not match the particular format. Negative samples may be used to test whether the computer program properly rejects samples not in the particular format.